Acoustic device



Oct. 13, 1931.

Filed sept. 2o. 'T928 :s sheets-sheet 1 W z5 ATToRN s V. A. SCHLENKER ACOUSTIC DEVICE Oct. 13, 1931.

Filed Sept. 20. 1928 5 Sheets-Sheet 2 m HHIHHMK I www! oct 13, 193.1- v. A. scHLENKER 1,827,114

ACOUSTIC DEVICE med sept. 2o. 192s s sheets-'sheet s zsvATToRNE d/ patented ct. 13,

lYasmin A. senr.iiiynjzna yor Roorinsmnn; New' from: l

' yacoyus'rrc DEVICE Applicaties mea s'ptember1 2o,'1`9`2a serial 110,307,238.

This invention' relates' to'an acousticde.- vice, such for example, asaymechanismfor driving anfacoustic diaphragmlfwhich mayv p be', lforV instance, the diaphragmv off a radio xloud speaker. VIt has for its princlpalfolnect y the provision of a generally improved mechanism of this character which 1s more' s1mplej and?v ehcient than those heretofore known. Another object of the invention 1s the pro- -'vision of a device/fof thiskind which 1s more compact than other similar devices previ-L ously used. y

Still another obj ectv is the provision 'of .an

r acoustic device having atransformer with a `co1nparatively "low secondary impedance.

Still another object is the provision of mechanism which will operate satisfactorilyvon a comparatively small inputfof power.

A further object of theinvention` is the'k provision of anl acoustic devicel such as a' radio loud speaker which ywill'give purer and `more accurate reproduction than other devices pre- I viously known. f f y 'l l To theseA and other ends the inventionv re-y "sides in certain improvements and' combina-y tions of parts, all as will be hereinafter morel fully described,` the novel features lbeing pointed out in the claims at the end of this v, specilic'ation. l f In the drawings:

structed in,l accordance with a bodiment of the invention Fig. '2' is a ,fragmentary section .taken sub-v stantially "on the linej22 of-Fig. 1; "1 Y Fig.v Sfis a plan of "the mechanism shown inFigl; 1 Fig. l is a view similarto Fig. 3'w1th parts in section, the section being takenv substan- 1- 40 Atially onthe line 4f40f Fig.` 1;

Fig. Fris' averti l l tially through the center of the-device; j

Y vFig. 6 is a perspective View of certain elec- 1 f havlnga conductor 'vibratlng 1nV the'air-gap,

trical conductors used in the device; Y

- tov6,-a11d Fig.I 8 isla perspective'view partly in sec#y Fig. l'is -an'A elevation of ak device con@r preferred eln-l l K f the bar of which the magnet is constructed bent inthe direction of its thickness' rather f the ring of the'magnen-and such a construcall section taken substan- Fig. 7 isa diagram illustrating the electra-'- f cal conductors of the form shown in Figs. 1

a' transformerof a slightly diiierentltype. l'

."Similar reference numerals throughoutthe several Views indicate the same partsl..

The' acoustic devlce of the present appli-V;

cation. is 'similar in some respects tothat 5i.

shown in my patent application filed August. 6, `1928, Serial No. 297,606. Thegeneral principles to be used.l in the designota magnet for use in anV acoustic device of this kind'are setforth at kvlength in said-application, and need not berepeated here;

yThe present device'includes, in general, a base 11 on which may be mounted a ypermanent magnet comprisinga 4bar 12, this bar being secured -to the basey 11 bythe Ushaped member 13 held. by screwslfl. This? bar is Abent -so as, to form" a somewhat ring-.like

lmember enclosing'a substantial area, in order to reduce the leakage flux; IThe ends ofthis bar 12 are indicated at'l in Fig. 2, and to. 70 these ends pole pieces 16 are secured by means suchas thebolts-17,y thel pole pieces having a comparatively narrow `air-gap between them,as is shown clearly in Figures 2 and 4. ]t will' be noted that thebar 12 has a cross section, one dimension of which is substantially longer thank another dimension. The longer dimension `may conveniently Ebe referred to as'thewidth of themagnet, while the shorter dimension may be termed ythe thickness thereon Forease of construction as well asfor a magneticallyeiiicientfmagnet,

when `bent into a` ringlike form should be than in the direction of its width.V 'Suchl a bending,'however, ordinarily results in maktion is illustrated, vfor example, in myi prior dynamic typeAv thi'sconductor would then extend substantial 95 ly -perpendi'cular'to the planev of the" magnet f ring, and if" an acoustic vdiaphragm werecon-4 nectedto this conductor in the usualmanner, the diaphragmwould also lieperpendicular to f ther-'planeV of the" ring, thus resulting in l a comparatively bullry construction taking up considerable space.

According to the present construction, an arrangement is provided which permits the diaphragm to lie in a plane parallel to the plane of the magnet ring rather than perpendicular thereto, thus resulting in a construction much thinner and more compact than.

`5,' is mounted to vibrate within the air gap between the pole pieces loin response to electric currents flowing through the conductor. rifhis mounting permitting such movement may include arms 2l on the conductor, the ends of these arms being attached to the free ends of. resilient plates 22, which plates have their opposite ends fixed. As illustrated in Figs. l and 5, six ot these resilient plates may be employed, three on one side ot the poley pieces l6,.and three on the opposite side. The two plates constituting the lower pair when.

viewed as in Figures l and 5 each have their upper edges fixed to cross bars Q3, which form I part of the electrical circuit, as will .be brought out below. The plates 22 of the intermediate pair each have their upper ends secured to cross bars 2e which are insulated from other parts of the device, while the plates of the uppermost pair are secured to the edges of a cross bar which terms partof the electrical circuit. rlhus the upper and lower sets of resilient plates Q2 constitute electrical connections leading` to and from the conductor 20. The mounting of this conductor on the resilient plates is, in general,

siiiiilar to the construction shown in my prior application above mentioned, and is claimed in said prior application, no v,claims to this construction per se being' made inthe present application.

Ylf desired, dampingpads 26 of telt or other suitable material may be secured tothe resilient supporting and guiding plates 22and preferably these damping members extend slightly past the edges ofthe plates, in the manner illustrated in my said priorapplication.

It will be noted that on account of the twist in the magnet, the conductor 2O lies-substantially in the plane ot the magnet ring, rather than perpendicular thereto as was the case in my said prior application. This arrangement ot the conductor allows the diaphragm to be connected directly and simply to the,`

neem 14 conductor, While permitting it to lie in a plane parallel to the plane of the ring, thus producing a desirable compact construction.

ln the present instance there is shown a diaphragni 30 having the saine general shape as that illustrated in my said prior application, this diaphragm having a ring 31 ot U-shaped crosssection secured thereto, which ring is connected to the movable conductor 20 by rltensions 32 on the conductor. rlhe peripliery of thesdia-ph-ra'gm 3() may be mounted, for example, on a strip of material 35 having slits 36 (Fig. l) therein, so that the strip may be curved to conform to the periphery of the diaphragm. The outer edge of this mounting strip 35 may be secured to an angular supporting,member 37 as shown in Fig. 5, and a strip. 38 or' sui-table resilient material, such as telt, may extend around this angular diaphragm supporting member and lie against a wall 39 forming part of the cabinet or case in which the device may be placed. The construction of the diaphragm and the manner in which it is attached to and operated by the conductor 20 may be in accordance with the disclosure of my said prior application.

It will be observed from Figs. 4 and 5 that the plane ot the periphery of the diaphragm isparalle-l to thev plane of the magnet ring, andthat thecenti'al portion of the diaphragm projects partly into what might be termed the thickness of the magnet, thus resulting in an unusually compact construction which may be4 placed. within aV comparatively thin cabinet or housing. In addition to the feature ot compactness, this construction is also advantageous because the magnet itself interferes less with the sound 4waves produced by the diaphragm than is the case when the plane of the magnet ring is perpendicular to the planeoi':l the periphery of the' diaphragm.

' In an acoustic device of this type, the best results are obtained when the transformer used in connection with the device has an extremelylowV secondary impedance, so that it will match as nearly as possible the low impedance of the conductor20-j An importantV feature of the present invention is the provimore satisfactory operation and more faithful reproduction than is possible with transformers havingr a higher impedance.

One possible form ot low secondary impedance transformer is illustrated especially in Figs. l, 5, 6,. and 7, and comprises a core iaving three legs indicated by the numerals 50, 5l, and .52'.` A primary winding 5,3 surrounds the central leg 50, the ends of this winding being connected to leads 54 (Fig. l) extending to jacks in which electrical plugs connected to any suitable circuit may be in serted.. It desired, one or more intermediate Vtaps may be. made in the primary winding. Eour leads 5,4 and jacks 55 are shown in ioe ias4

sion of such a transformer, which results in l Fig. 1, two of -thesebeing?connectedto4 the p extreme ends" of v.theprimary ywinding' 53, l f while'` the vother tw'o frepr'esent" intermediate taps.

the flux yf geiierated'bythe primary winding 53, these conductingmembers preferably be-vr fing connected with each-ether in parallehand inseries with the air gap conductor 20. For instance, one of these conductors may include a bar or strip 55 extending between the middle leg 50 and tl'i'ejlower leg 52 of thetransformer, one end-of this strip? being connected by strip 56 with the 'bar 25 on'which the topmost pair of resilient plates 22=is mounted.4 The? opposite end'ofthestrip25 may befattached `toy a conducting strip 57 which leads' in turn ato strips 58 jwhicha're connected to the cross pieces 23' on which the lower pair of resilient* plates 22f`isinounted. Thus the strip y55 links a part of Atlielflux producedby thevprimary winding-53 (namely that part" which iiows :through the lower leg A52. of the core) and is y connected in 'series with the conductor 20,fso2

that: currents induced in this strip 55 will flow through theconductor. v f y '1 Another part Vofthe secondary winding may include a strip 60 4extending through the transformer betweenthe middle leg l and the upperlegr51 andbeing 'connected atone end to la downwardly extending' strip' 61,

which' leads to strips 62"connectedl toy the.' cross 'bars 23 which support the resilient plates i 2201:' the lower pair. 'Theopposite end .of` this strip 60`is connectedy to a'downwardly n extendii'ig strip 63 whichv passesl close to the strip 57 lbut wliichiszins'ulated therefrom by, a klayer of insulating inaterial'Gl.' The lower end of this strip 63 is connected to thecross piece 25k which supports `the resilient plates 22 ofthe -upper'pair.- 1 i Itwill be-seenztha't the strips 60,61 and 63 I constitute a secondary winding link-ing a part ofthe fluxproducedby the primary winding, this part being equivalent tothat pro-` portion of the flux which passes through thel upper leg 51 of the transformer. This portion ofthe .secondary winding is connected in seriesv with-the air gap conductor 20, aswill.

be observed, and inalparallelwith the other portion k of the secondary winding. Since each ofithe two portions 5,5V and of the secondary :winding link yhalf-ofthe flux producedfby thefpriin'ary winding, and since*` these'y two portionsy are connected in parallel rather than in series, it follows'lthatas far as the/impedance ratio is concerned, the transformer is equivalent to lone ofthe conven tional type having ay .primary of :the same number of turns as ishere used andhaving a secondarywinding ofonly half; a turn..y By

using a'transforineirof this kind in an acoustic'- device of this nature, the primaryr can. be

p The secondary winding, in thepresent inf stance, comprises a plurality of conducting members each of'whfichlinks .only a' part of f made of proper sizeto match'asnearas ypos-1 sible the impedance of the tube to which the 1 primary is connected, Whilet-he secondary lcan be made `to match satisfactorily theeXtremel-ys g low*y impedanceofthe conductor T20, thus vre-` sulting in superior-'reproduction andreqiiir-gy king only a comparatively small ,power` input.-

The strips 55'and 60 of the secondary winds? course, insulated from the.trans-;

fnrmer core by any suitable means, such as the layers 66 of yinsulating material.. Thecrossi bars24 which support the resilient plates 22 of the` middle pair formnopart of theelec-l` ing are, o

trical circuit, and arein'sulated from the pole trated. Blocks 7 4 of insulating material are inserted between the sections` oftheV core and act as spacers-tokeepthem apart, as is plaiir-V lv shown. lA primary winding; 75 extends around all three of the core sectionsgTlie secondary winding comprises a pluralityof conductingI members each linkingv a part onlyV` of the flux .generatedfby the primary-wind? ing, these'conducting membersbeing connectedwitheacli other in paralleland in series with the vibrating conductorintlie air, gap,v

these ,U-shaped strips extending aroundv one ofthe sections of the transformercercas-is clearly illustrated, so that-each strip ,links part only of thevfluX inthe whole core, The `long legs 76 of the three Uj-shapied members In they construction illustratedby way of vexample. in Fig; 8, the secondary ,windingv comprises three U-shaped strips each having along leg 76 anda shorter leg` 77 each of.;

licei may be connected to each other by a plate 78, 'Y v Whilel .the shorter Llegs 77 may y likewise 'be connected to each other by rods 79 ,which'exfv tend through openings in thel legsq76 so that they do not coineinto electrical contact there-y with.

Thus

the vibrating conductor 20 by suitable leads 80. It will be understood, of course',thatthe f transformer core may be splitiinto any suit# able number' of sections, three ofV these being f the three sections of Itliel n secondary winding are connected to each otherfin parallel,V and they may be connectedin'series with" shown simply by way-,ofv example A construction of the type illustrated lisl equivalent. from an impedance standpointto akconveiif; tional transformerhaving afprimary. ofthe. same number of .turns shown and havinga. secondary .winding yof onl 3 one-thirdofv, .a turn. [Obviously the trans v ormercoregcould *out in a number of ways.

be split intoany number' of 'sections desired. If four sections were used, the secondary winding would be equivalent to a quarter @t a turn, while if five sections were used it would be'equivalent to a fifth of a turn. Thus nected to the primary winding of either of the transformers disclosed above, in which case the diaphragm 30 will be caused to vibrate in accordance with the audio-frequency waves. If desired, the operation of the ap- :paratus may be reversed, sound waves falling` upon the diaphragm 30 being caused to vibrate this diaphragm and to move the 00nductor 20, thus producing'corresponding electrical impulses in the primary winding. Likewise, a phonograph stylus can be attached to the conductor $20, and` made to vibrate the same, so that the device may be employed for a phonograph pick-up.

` Any suitable framework may be used for supporting the various parts of the apparatus. A convenient arrangement, as shown particularly in Figs. 1, 3, and F includes upright angle bars having horizontal eXtensions 86 and 87 at their upper and lower ends respectively, the ends of these horizontal extensions being secured by means such as screws S8 to the angular frame 37 which eX- tends around the periphery of the dia'- phragm. The transformer may be supported bv the members 85 and 86. The bolts 17 which attachthe pole pieces to the magnet bar 12 extend through the upright angle members 85, as shown in Figs. l and 2. Preferably three bolts are used to attach each pole piece 16 tothe magnet bar, and if depermits each pole piece 16 to be bolted conveniently to the magnet bar 12vby means of the middle bolt 17, and the frame members 85 may later be assembled on the pole pieces and Vsecured to them and to the magent bar 12' by the upper and lower bolts 17.

While certain embodiments of the invention have been disclosed, it is to be understood that the inventive idea may be carried This application is therefore not to be limited to the precise details shown, but is intended to cover all variations and modifications thereof falling within the spirit of the invention, or `theV scope of the appended claims'.

Lezama I claimv as my invention: 1. Anacoustic device comprising a magnet having an air gva-pf, a conductor mounted for .movement within the air gap, a transformer having a flux-generating winding, and a conducting member linking a part only of the flux generated by said winding, said conducting member being electrically connected to the conductor in the air gap.

2, An' acoustic device comprising a magnet having an air gap,- a conductor mounted for movement within the a-ir gap, a transformer having a flux-generating winding, a conducting member linking a part only of the flux generated by said winding, and a second conducting member linking another part of said flux, said two conducting members being connected in parallel with each other and in series with the conductor in the air gap.

8. An acoustic device comprising a magnet having an air gap, a conductor mounted for movement within the air gap, a transformer having a linx-generating winding, and a plurality of conducting members each linking a part only ofthe flux. generated by said winding, said conducting members being connected in parallel with each other and being electrically connected to the conductor in the air gap.

ll. A radio loud speaker comprising, in combination, a magnet having an air gap, a conductor mounted for movement within said air gap in response to electric currents flowing through said conductor, an acoustic diaphragm connected. to said conductor to be moved thereby, and a low secondary impedance transformer including a flux-generating primary winding and a secondary winding comprising a plurality of conducting members each linking a part only of the flux generated by said primary winding, said conducting members beii'ig connected in parallel with each other and in series with the conductor in the air gap, whereby said diaphragm will be vibratedv in accordance with electric currents impressed upon said primary winding.

5. A radio loud speaker comprising a magnet formed of a bar bent into a ring-like shape and having an air gap, a conductor mounted fer movement within saidl air gap in response to electric currents flowing through said conductor, said conductor lying` substantially in the plane ofthe ring, and an acoustic diaphragm connected to the conductor to be moved thereby, the periphery of said diaphragm lyingl substantially ina plane parallel .to the4 plane of the ring,V whereby to pro fide a comparatively thin and compact device.

6. An acoustic device for transforming electric waves into sound waves or vice versa, comprising in combination a magnet having an air gap, a conductor mounted for movephragm operatively connected to said conductor for movement therewith, a trans-V former core divided into a plurality of sections, a primary. winding encircling all of said sections, and a secondary winding comprising a plurality of conducting members each encircling only one of said sections and being connected in parallel withL each other and in series with the conductor in the air? gap, to provide a secondary winding of low impedance, substantially matching the impedance of said conductor.

7. An acoustic device for transforming f electric waves into sound waves or v1ce versa,

comprising in combination a magnet having an air gap, a conductor mountedrfor movement within said air gap, an acoustic dia-i phragm operatively connected to said con-r ductor for movement therewith, 'aA transformer core having a plurality of winding legs including at least two legs through which only a part of the flux passes, a primary winding for producing flux in said legs, and` a secondary winding comprising a plurality of conducting members each encircling only onel of said legs through which only part o of the flux passes, said conducting members c being connected in parallel with each rother y and in series withthe conductor in the air gap, to provide a secondary winding of low impedance substantially matching the im-v pedance of said conductor.

8. A. radio loud speaker comprising a magnet formed of a bar substantially wider than its thickness,'said bar being bent into a ringlike shape having an air gap therein, the intermediate portion of said bar having its width substantially perpendicular to the plane of the ring, the ends of saidbar adjacent'l the air gap being twisted so that at the air'gap the width of said bar lies subl stantially in the plane of the ring, a conductor lying substantially in the plane of the ring' and mounted for movement within said air gap in response to electric currents flowing through said conductor, and aV relatively large direct-actingv acoustic ldiaphragm operatively connected to said conductor to be ymoved thereby, thev peripheryof said diaphragm lying substantially in a plane parallel to the plane of the ring to provide a comparatively thin and compact device.

` VESPER A. SCHLENKER. 

